Disc type recording media (hereinafter referred to as “optical disc”) such as DVD (Digital Versatile Disc) and CD (Compact Disc) to which optical reading is applied have rapidly become widespread as an application for storing a computer-file and a moving image stream. An optical disc has a large memory capacity and can be accessed at random. Further, the optical disc has no possibility of the wear and corruption of a recording surface due to reading, a head-crush, and the like different from a contact type magnetic recording medium. Further, the disc surface is strong and has a low degree of danger of incidentally losing data. Recently, the optical disc is widely used as an external recording medium for a computer and as an external memory device.
For example, UDF (Universal Disk Format) (registered trademark) defined by the OSTA (Optical Storage Technology Association) is known as an optical disc-format with high compatibility (refer to, for example, Non-Patent Document 1). UDF corresponds to a mounting technology of ISO/IEC 13346 standard which is also known as ECMA-167 (refer to, for example, Non-Patent Document 2) (ISO/IEC 13346 is a successor of ISO 9660 corresponding to an increase of a disc capacity and the number of files). In the 1990s, UDF became widespread as an application of a writable optical disc as the cost of a CD-RW medium and a CD recording apparatus is reduced.
UDF can execute processing for adding and deleting a file to an optical disc through an ordinary file system by employing a packet write system. The packet write system, to which reference is made here, writes data as a packet structure by providing a link block and four Run-In areas in front of user data as well as providing two Run-Out areas at the end of the user data. Seven blocks are used as a linking area which is a joint area between adjacent packets in addition to a user data area. UDF is a file system to which data can be written from almost all the operating systems (OS) as well as a file written thereto can be compatibly replayed on the operating systems without a special read program and can manipulate the contents in an optical disc by a method similar to a hard disc, floppy disc, USB (Universal Serial Bus) flash memory.
UDF defines four types of accesses, 1: Read Only, 2: Write Once, 3: Rewritable, and 4: Overwritable are prescribed as the accesses of an optical disc. Among them, when user data is recorded to a type 4 overwritable optical disc of according to UDF, there is exemplified a method of using a space bitmap descriptor (SBD), in which an unused status of each area is described by a bitmap format, to manage a space area in a partition for recording file data (refer to, for example, Patent Document 1).
Although SBD can be optionally disposed in a partition, a partition descriptor (PD), in which point information is described to point out the location of SBD, is described in a volume descriptor sequence (VDS) which describes information as to the contents of a volume structure. Although VDS can be also optionally disposed in an area outside of a partition, AVDP (Anchor Volume Descriptor Pointer) composed of point information for pointing out VDS is defined. Accordingly, SBD can be referred to through AVDP, VDS, and PD.
Here, when user convenience is taken into consideration, it is preferable to sequentially take out a recording medium on which data is overwritten according to UDF from a disc recording apparatus and to replay it also by a replay only apparatus. This is, for example, to take out a still image, moving image, and the like picked up by a digital camera and recorded to a DVD, to display and output images by loading the DVD on a DVD player, and to record picked up images by loading the DVD on the digital camera again.
However, in a UDF format of the version number 2.5 and later, since it is prohibited to record SBD in an optical disc having the access type 1, that is, in an Read Only optical disc, a problem arises in that a type 4 disc has no compatibility between a data recording apparatus and a replay only apparatus.    [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2000-112832    [Non-Patent Document 1] http://www.osta.org/specs/index.htm    [Non-Patent Document 2] http://www.ecma-international.org/publications/standards/Ecma-167.htm